Identification of flow regime in a slurry bubble column by Hilbert-Huang transform analysis

Experiments were conducted in a two-dimensional (2-D) slurry bubble column, which had a length of 0.1m, a width of 0.01m and a total height of 0.8m. The gas phase was oil-free air, tap water was used as the liquid phase, glass powders with particle diameter of 58μm-75μm constituted the solid phase, which belonged to the Geldart A particles. Time-domain analysis and the Hilbert-Huang transform methods were employed to analyze the differential pressure signals obtained and to identify the transition points of the flow regimes in the slurry bubble column. Useful qualitative and quantitative information about the changes in flow structure and particle distributions were extracted. Changes in the standard deviation, skewness and flatness of measured pressure time series with superficial gas velocity are proposed. Hilbert-Huang transform was applied to extract information from signals, and flow structures of the slurry bubble column were characterized by the energy distribution of the multi-resolution signals and the EMD energy entropy. Particle distributions were obtained and analyzed from flow pattern images.